Some of the shift is driven by visceral distrust of President Barack Obama, who is the one proposing military strikes against Syria. Some is driven by remorse and lessons learned from the Iraq war. And some is fed by the isolationist and libertarian strains of the grassroots tea party movement.

Plenty of Republicans, including key congressional leaders, support Obama’s push for military action against the Syrian regime for allegedly using chemical weapons. But among constituents, rank-and-file members of Congress and many influential voices in the party’s echo chamber, the trend is decidedly anti-war.

“There is a growing isolationist movement within our own party,” said John Weaver, an Austin, Texas-based Republican consultant.

The party’s popularity surged in the late 1940s partly because of its unrelenting stance against communism. Republicans nominated World War II hero Gen. Dwight D. Eisenhower as its 1952 presidential candidate and he won two terms. Ronald Reagan’s presidency is still revered by supporters for his tough talk against the Soviet Union, and in his 2005 inaugural address, President George W. Bush redefined America’s international mission.

In 2008, GOP vice presidential candidate Sarah Palin was an impassioned supporter of the Iraq war. Now, in a Facebook post titled “Let Allah Sort It Out,” she argued against military action in Syria. “If our invasion of Iraq wasn’t enough of a deterrent to stop evil men from using chemical weapons on their own people, why do we think this will be?” she asked.

And while former Vice President Dick Cheney was a leading advocate of invading Iraq, his daughter Liz, now seeking the Republican Senate nomination in Wyoming, told a tea party gathering earlier this week that she would vote against a Syria strike. Obama, she said, has taken “an amateurish approach to national security and foreign policy,” according to the Jackson Hole News & Guide.

At the Heritage Foundation, a conservative think tank in Washington, researchers in November lashed out at Obama for not being tough enough on the Syrian regime of President Bashar Assad.

“American policy toward the Syrian uprising has been an unmitigated failure. President Obama’s glacially slow and overly cautious policies that were intended to avoid turning the Syrian uprising into a wider regional affair have had exactly the opposite effect,” Heritage said. “In order to keep this situation from crumbling further, the United States and its allies should work to facilitate government transition when the Assad regime falls. . . . Action must be taken sooner rather than later.”

On Wednesday, the group’s new tea party-inspired political operation, Heritage Action, lashed out at Obama for proposing airstrikes against the same regime.

“Heritage Action is opposed to punitive missile strikes on the Syrian regime,” the group said. “There is not a vital U.S. interest at stake. Further, there is not a clear, achievable, realistic purpose to the use of force being contemplated by the Obama administration, and officials offered little evidence such action would prevent further abuses.”

Some analysts see anti-Obama sentiment driving the change of course.

“If this were a Republican president making the exact same case, more Republicans would be supportive,” said Justin Logan, director of foreign policy studies at the libertarian Cato Institute.

Republicans said Obama does get a different reaction, but only because he’s got a different track record on foreign policy and the military.

Sen. James Inhofe of Oklahoma, the top Republican on the Senate Armed Services Committee, in 2007 pushed for a deeper military commitment in Iraq. “Let’s do it right,” he wrote. Now, he says, “the state of our military today cannot afford another war.”

Donelle Harder, Inhofe’s spokeswoman, explained Friday that the positions are consistent, and the senator has not changed his view that America needs a strong military. “He would say that if we had a Republican president, he wouldn’t have done to the military what President Obama has done,” she said.

Rep. Jeff Duncan, R-S.C., said he cannot trust the president in light of past foreign policy actions.

“The administration has a serious credibility issue with the American people due to the unanswered questions surrounding the terrorist attack in Benghazi almost a year ago,” said Duncan, recalling last year’s attack on a U.S. consulate in Libya. Duncan also cited questions about activity at the Internal Revenue Service and the National Security Agency.

Even Republican leaders backing Obama can’t resist a jab.

“Frankly, two years of mixed signals from the Obama administration, misplaced focus and a routine lack of outreach to members of Congress have fueled pessimism in this mission. I share that frustration,” House Majority Leader Eric Cantor of Virginia wrote in Friday’s Richmond Times-Dispatch.

“But it’s not just the president’s credibility that is on the line; it is America’s leadership in a troubled world that is in question.”

The grassroots tea party movement is helping to rally opposition.

“No one in the administration has come up with an endgame. What is the actual purpose?” asked Michael Openshaw, spokesman for the North Texas Tea Party. “We as tea party people find it extremely difficult to support this effort.”

Lawmakers with ties to the movement find strong opposition.

“I am all too aware that many Mississippians have zero desire to engage in another conflict in the Middle East,” said Rep. Steven Palazzo, R-Miss., elected in 2010, when the tea party helped Republicans win control of the House.

“When no compelling American interests exist, we should not intervene. No compelling interests exist in Syria,” said Sen. Rand Paul, R-Ky. His father, Ron, then a Texas congressman, was one of six House of Representatives Republicans to vote against the Iraq war in 2002. Sens. Ted Cruz, R-Texas, and Marco Rubio, R-Fla., also plan to oppose the current effort to strike Syria.

The trend in the Republican Party, said Weaver, seems pointed toward the anti-war crowd, and that could mean political danger for the party. Said Weaver: “We could give up national security as an advantage for the first time since Eisenhower.”